1. Field of the Invention
This invention relates to a system and a method of distinguishing multiple touch points and more particularly relates to a system and a method of distinguishing multiple touch points applied to an optical touch system.
2. Description of the Prior Art
Recently, image display technique is constantly innovated. A touch screen that has an interactive human machine interface (HMI) provides direct message input for users. It has been part of an electronic product, such as ticket terminal, projector, lottery terminal or industrial automation system, introduced actively by associated manufactures.
When a user touches a screen by his finger, the finger blocks the light relative to a certain position of the screen and then an image captured by a camera unit has a dark area accordingly. A general technique of optical touch screen achieves the input purpose by transferring the position of the dark area in the image into a coordinate on the screen corresponding to the dark area. In general, the optical touch technique can correctly detect a single touch point. However, once the user indicates two or more touch points on the touch screen at the same time, incorrect coordinates of the touch points may be obtained to the touch screen. As shown in FIG. 6, when there are two touch points on the touch screen, the system calculates two set of touch points (Pa, Pb) and (Pa′, Pb′). The incorrect coordinates therefore may be obtained.
In addition, for the camera unit, when one of the touch points is shaded by the other one (i.e. only a single shaded point or dark area on the captured image), it is difficult to calculate exact coordinates of the touch points respectively because of a lack of enough information of the touch points provided by the captured image.
In view of the above, the invention provides a system and a method of distinguishing multiple touch points.